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fix floating comparison in path.arc #26991

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fix floating comparison in path.arc #26991

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19c0e07
fix floating comparison in path.arc
stevezhang1999 Oct 4, 2023
2196b0f
handle edge case when theta1=0; add tests
stevezhang1999 Oct 5, 2023
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9 changes: 8 additions & 1 deletion lib/matplotlib/path.py
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Original file line number Diff line number Diff line change
Expand Up @@ -943,13 +943,20 @@ def arc(cls, theta1, theta2, n=None, is_wedge=False):
polylines, quadratic or cubic Bezier curves
<https://web.archive.org/web/20190318044212/http://www.spaceroots.org/documents/ellipse/index.html>`_.
"""
# we want to get the same result when the input changes within [-tol, tol]
# this behavior is only for internal use to offset floating-point error
# so it should not be relied on by the user
tol = 1e-6

halfpi = np.pi * 0.5

eta1 = theta1
eta2 = theta2 - 360 * np.floor((theta2 - theta1) / 360)
# Ensure 2pi range is not flattened to 0 due to floating-point errors,
# but don't try to expand existing 0 range.
if theta2 != theta1 and eta2 <= eta1:
# condition: theta1 != theta2 and eta2 <= eta1
# implementation note: use np.isclose() may break when theta1 = 0
if abs(theta1 - theta2) >= tol and (eta2 <= eta1 + tol):
eta2 += 360
eta1, eta2 = np.deg2rad([eta1, eta2])

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16 changes: 16 additions & 0 deletions lib/matplotlib/tests/test_path.py
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Expand Up @@ -475,6 +475,22 @@ def test_full_arc(offset):
np.testing.assert_allclose(maxs, 1)


@pytest.mark.parametrize('offset', range(-720, 361, 45))
def test_full_arc_rounding(offset):
# GH 26972 - edge case for floating point rounding
# we want get the same result when input of arc
# changes within [-tol, tol], where tol = 1e-6
tol = 1e-6
low = offset
high = 360 + offset + tol

path = Path.arc(low, high)
mins = np.min(path.vertices, axis=0)
maxs = np.max(path.vertices, axis=0)
np.testing.assert_allclose(mins, -1)
np.testing.assert_allclose(maxs, 1)


def test_disjoint_zero_length_segment():
this_path = Path(
np.array([
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